Rechargeable lithium-organic electrolyte batteries are now being developed to provide low cost, high energy density power sources for communications, night vision and other applications. Typically, a rechargeable lithium-organic electrolyte battery is comprised of a lithium anode, a cathode including compounds such as titanium disulfide (TiS.sub.2), molybdenum oxide (MoO.sub.3), chromium oxide (Cr.sub.2 O.sub.3), vanadium oxides (V.sub.2 O.sub.5 and V.sub.6 O.sub.13), vanadium sulfide (V.sub.2 S.sub.5) etc. and an electrolyte solution including a lithium salt such as lithium perchlorate, lithium hexafluoroarsenate, lithium tetrachloroaluminate etc in an organic solvent such as propylene carbonate, dioxolane, diethyl ether, sulfolane, tetrahydrofuran, 2-methyl tetrahydrofuran, etc.
One of the problems common to rechargeable lithium-organic electrolyte batteries is the oxidation of the organic solvent during the overcharging of these cells resulting in the degradation of electrolyte solutions.
There are two ways of dealing with the "overcharging problem". One approach is to monitor and regulate the voltage of each individual cell in the battery. That approach is deemed relatively complex and costly. The second approach is to introduce an electrochemical couple capable of accepting and dispersing excess charging energy delivered to a cell. In this connection, promising results have been obtained using the lithium iodide/iodine couple. That is, during overcharging of lithium-organic electrolyte cells, lithium iodide is oxidized at about 2.79V to iodine and thereby prevents the oxidation of the organic solvent that occurs at potentials above about 4 volts. Iodine formed in the above reaction chemically reacts with lithium metal to regenerate lithium iodide in solution. Thus, the lithium iodide/iodine shuttle mechanism provides overcharge protection in rechargeable lithium-organic electrolyte cells.
The difficulty is that the oxidation of lithium iodide in organic electrolyte solutions occurs at potentials of about 2.8V which is close to the charging potentials of most of the cathodic materials and this interferes with the charging process.